The annealing of an ion implanted III-V compound poses a problem where one of the constituents exhibits a high partial vapor pressure. Various capping techniques have been described in the prior art.
During the relatively high temperature annealing cycle for GaAs with Si implanted at a surface, the surface will decompose, due to the large partial pressure of As, if specific precautions are not taken. Heretofore, specific precautions have been such as capping with Si.sub.3 N.sub.4 or AlN. Those capping films are directly applied to the surface and any thermal expansion mismatch results in undesirable surface strain on the GaAs. The implants are very shallow, about 2000 A, for MESFET (metal-semiconductor field-effect transistor) application, and the surface quality is of extreme importance for the electrical behavior of the active layer. Another drawback of the prior art use of surface capping films is that frequently trace contamination by oxygen makes them permeable for Ga, which results in stoichiometric changes of the GaAs ion implanted surface layer.
The prior art does not disclose annealing an ion implanted GaAs wafer in close proximity to a piece of InAs. In the prior art, Anderson et al, U.S. Pat. No. 4,135,952, discloses annealing ion-implanted gallium arsenide wafers by enclosing the wafer in a liquid-tight but gas-porous container, immersing the container in a saturated solution of gallium arsenide in gallium, and maintaining the solution at the annealing temperature. Further, Fuller et al, U.S. Pat. No. 3,070,467, teaches preventing the evaporation of arsenic from gallium arsenide semiconductor materials during the heat treatment thereof by placing the gallium arsenide body near a quantity of solid arsenic in a sealed quartz tube and heating the tube within the range of 800.degree.-1220.degree. C.